Because of its origin (natural gas) and a relatively high degree of purity, the gas used nowadays in the public network is in itself virtually odorless; if leakages are not noticed in good time, explosive gas/air mixtures with a high hazard potential quickly form. For safety reasons, gas is therefore odorized by adding odorants. For example, in Germany it is stipulated that all gases which do not have sufficient intrinsic odor and are distributed in the public gas supply (DVGW-Arbeitsblatt [Worksheet] G 260) are odorized in accordance with DVGW-Arbeitsblatt [Worksheet] G 280; DVGW=Deutscher Verein des Gas-und Wasserfaches e.V. [German Association on Gas and Water], Eschborn. These odorizing compositions are detectable even when highly diluted and, because of their extremely unpleasant odor, act, as is desired, as a warning signal for people. In Germany, approximately 90% of service gas is currently odorized with tetrahydrothiophene (THT) (12–25 mg/m3); in addition, odorization using mercaptans or thioethers is also customary.
THT and mercaptans are highly suitable for reliable odorization of gas. However, in the context of treating the environment with more respect, it is to be noted that during the combustion of such odorized gases, sulfur dioxide forms as combustion product—only in small amounts at each individual combustion site, but, viewed on a countrywide scale, in amounts of a few hundred tons per year. It would be desirable to overcome this disadvantage; however, a number of requirements have to be satisfied:    1. The odor must be unpleasant and unmistakable (odors from kitchens and homes are excluded). It must act as a warning signal for people who smell escaped gas.    2. Everybody with an average sense of smell and average physiological condition must be able to detect the odor.    3. The warning odor stage (=average odor intensity) must be achieved before the ignition limit or a kinetic carbon monoxide content is reached.    4. The odorizing composition must be as nontoxic as possible and must not form any toxic combustion products.    5. The odorizing composition must have high volatility and evaporate leaving as little residue as possible.    6. A suitable odorizing composition must not condense at winter temperatures, nor separate, nor adhere to metallic pipes.    7. The odorizing composition must combust without leaving a residue.    8. The odorizing composition must be storage-stable and chemically resistant to the gas and to the plants. It must not promote corrosion, nor attack customary seals.
Attempts have already been undertaken to provide new gas odorizing compositions. Thus, the following, for example, have been proposed:                alkyl acrylates, vinyl or alkyl ethers and mixtures thereof (JP 76-7481),        n-valeric acid, optionally in combination with ethyl acrylate and/or triethylamine (JP 76-34 841),        mixtures of sulfur compounds and aliphatic aldehyde (JP 78-35 562),        cycohexene (JP 83-42 235),        norbornene derivatives (JP 87-1998) and        saturated ethers, saturated esters, and mixtures thereof with mercaptans.        